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Technical Report #19 - Chelsea Center for Recycling and Economic ...

Technical Report #19 - Chelsea Center for Recycling and Economic ...

- development of

- development of economical collection, sorting, and cleaning systems for postconsumerplastics and wood productsThis effort most likely should be coordinated by the Department of Plastics Engineeringat the University of Massachusetts Lowell, working in cooperation with the Forest and WoodProducts Institute. Participation of the Chelsea Center relative to the use of recycled materialsalso would be important.Efforts are currently underway to begin a wood-plastic composite laboratory in conjunctionwith a proposed integrated biomass utilization and research facility. The facility would beoperated in conjunction with the Forest and Wood Products Institute at Mount Wachusett CommunityCollege. Besides the wood-plastic composite laboratory, the facility would include anexperimental sawmill and a secondary wood products manufacturing facility to produce furniturepanels and other products from underused wood species and sawmill residues for applied researchand demonstration purposes.Umass Lowell's participation in the composites laboratory would open the possibility ofgrant funding for both wood and plastic doctoral and post-doctoral graduate student involvementin the project. Project guidance by the scientists of Umass Lowell who possess the required researchand technical expertise in composite technology would enhance the viability of the project.Government, educational institutions, and industries need to form partnerships to maximizeresearch and development, leverage funding, and facilitate technology transfer.IX. REPORT OF A LABORATORY EXPERIMENTThe following section reports on a laboratory experiment conducted by Dr. Robert Malloyand Siddharth Shroff of the University of Massachusetts Lowell, Department of Plastics Engineering.This research presents differences in using polyolefins versus polyesters in woodthermoplasticcomposites. Due to the difficulties of using PET is such applications, a laminationprocess is proposed.1. IntroductionThere have been many studies conducted on the use of wood fiber as a reinforcement forboth virgin and reinforced thermoplastics (see research briefs in Appendix N). Wood fiberthermoplasticcomposites can be durable, stiff, and economical. Wood fiber offers significanteconomic advantages compared to other reinforcements such as glass fiber. However, there are anumber of potential issues that must be addressed for wood fiber thermoplastic composites.The cost of incorporating or compounding the wood fiber into the thermoplastic can besignificant, as intensive melt compounding (e.g., twin screw extrusion, etc.) is usually required.As with any compound, good dispersion of the additive is required if optimum properties are tobe obtained. It is difficult to obtain the required level of dispersion using lower cost single screwextrusion equipment when producing wood fiber-thermoplastic composites. Unlike glass fiber,wood fiber must also be predried prior to melt compounding in order to remove as much moistureas possible, as most wood species are very hygroscopic.Another significant problem associated with the use of wood fiber is limited adhesion tothe thermoplastic matrix. Composite theory dictates that some degree of adhesion is required42

etween the reinforcing fiber and thermoplastic matrix. As with glass fiber reinforcements, theadhesion between most polymer matrices and the reinforcing wood fiber is limited. Many studieshave shown that pretreating the wood fiber with a coupling agent (as is done with glass fibers)prior to melt compounding will improve stress transfer between the wood fiber and thermoplastic.Alternatively, other studies have shown that a third material component (such as a compatibilizer)can be added with the wood fiber and thermoplastic in order to enhance the performanceof the composite. The latter technique is significantly easier as no additional material processingsteps are required; however, this method maybe less effective relative to fiber pre-treatment witha coupling agent.Another very significant problem associated with wood fiber-thermoplastic composites isthe very limited thermal stability of most wood fibers. Unlike glass fibers, which are stable totemperatures in excess of 1000 degrees F, well above the processing temperature of any thermoplasticor thermosetting material, wood fibers show signs of degradation (smoke, odor, darkeningcolor, etc.) at the processing temperatures of many thermoplastics. A review of the literature (seeAppendix N) has shown that the widely used thermoplastic resins for wood fiber-thermoplasticcomposites are lower processing temperature materials such as low density polyethylene (LDPEor LLDPE), high density polyethylene (HDPE), polypropylene (PP), polyvinyl chloride (PVC)and polystyrene (PS). All of these thermoplastics process at temperatures in the 350-400 degreesF range.Using these lower melting point resins, it is possible to produce wood fiber-thermoplasticcomposites (such as wood fiber-HDPE) with good toughness, but of limited stiffness. Limitedstiffness and perhaps more importantly, limited creep resistance (long-term stiffness) is one ofthe most significant problems associated with wood fiber-thermoplastic composites. This is becausemost of the lower melting temperature thermoplastics have limited stiffness, are brittle,and tend to become even more brittle when wood fiber is added.2. Wood Fiber-Polyethylene Terephthalate (PET) CompositesThe purpose of this experimental study was to explore the use of recycled PET (regroundand cleaned beverage bottle flake) as the thermoplastic binder for a wood fiber composite. RecycledPET is widely available and has excellent stiffness and creep resistance relative to thepolyolefin binders more commonly used for wood composites. PET is also very polar and shouldexhibit a significantly better degree of binding with the cellulosic wood fibers compared withpolyolefins. Unfortunately, PET has a melt processing temperature in the 500 to 550 degrees F(260-288 degrees C) range, well above that of the polyolefin (PE or PP) binders more commonlyused for wood fiber-thermoplastic composites. Conventional wood fiber composites based onHDPE and PP were prepared for control purposes.Several wood fiber-plastic compounds were prepared using (1) recycled fractional meltindex HDPE, (2) recycled injection molding grade PP homopolymer, and (3) PET, as the binders.Two grades of untreated wood fiber (short and long fiber) were used as the reinforcement ata concentration of 30%. The polyolefin formulations were prepared as conventional control formulations.The primary purpose of the study was to determine if it is feasible to prepare a woodfiberreinforced PET composite.Conventional twin screw melt compounding of such a composite is not possible becauseof the very high melting temperature of the PET (resulting in excessive wood degradation). As a43

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